Morbidity and diagnostic yield of Deep Venous Thrombosis (DVT) and Pulmonary Thromboembolism (PE) increase day by day. The PE, as the most serious complication of the DVT, has a higher morbidity and case fatality rate. It was reported in literature that the yearly morbidity of DVT in the total population in western countries was between 0.05% and 0.1%, and there were about 30 million patients having DVT and sequelae in China. Due to a potential risk of a fateful Pulmonary Embolism (PE) caused by caduceus blood clots, it has become a difficult problem of a clinical treatment. An application of an Inferior Vena Cava Filter (IVCF) not only may effectively avoid pulmonary embolism, but also makes thrombolysis and surgical treatment safer. It was shown by an analysis that a placement of the IVCF could effectively prevent PE, and decreased the PE incidence rate of DVT patients from 60%-70% down to 0.9%-6%, and the incidence rate of fateful PE down to 0.7%-4%. Due to effective PE prevention, a small operative wound, simple operation and few complications, the IVCF has been regarded as a preferred method for preventing PE.
The Inferior Vena Cava Filter (IVCF), an instrument formed by weaving metal wires or carving a whole metal block by lasers, is placed in the inferior vena cava by a special conveying device to form a reticular protection structure for obstructing large blood clots. A common inferior vena cava filter includes fine support rods generally made from super-elastic nickel-titanium alloys. The present IVCFs may be classified into recoverable and permanent implantation filters, where the permanent implantation filters may result in lifelong use of anticoagulants or other complications because they are placed in the human body for a long period of time. It can be seen from clinical application data of IVCFs implanted into the human body for 5 years that the ratio of the permanent filters is gradually reduced and the recoverable filters have been preferred by patients. The present recoverable filters are mainly realized in structural design. For example, in Chinese Patent No. CN2569770Y, Y-shaped rods are designed on a conical surface net end, which was convenient for filter recovery; Chinese Patent Publication No. CN1868549A employs an opening design, where a spiral funnel shape was formed by metal wires and a plurality of metal wires were radially woven; other Chinese Patents (Issued Nos. CN2710575Y, CN200942133Y, CN201088640Y, among others). also realize the recovery of filters in structural design. All the above filters use structure to change the recovery time as a technical solution. Although the recovery rate and recovery time window of filters may be improved to a certain extent, the embedding of cells on the surfaces of the filters and degree of endothelialization cannot be basically inhibited. Meanwhile, as the majority is based on unsymmetrical single umbrellas in this design, such a structure has a poor geometric stability, and the filters are likely to generate displacement and inclination. Furthermore, the poor geometric stability also results in the rod crack of filters and the damage to vessel walls during recovery.
Seen from main manufacturers of recoverable filters in the world, the patents of Cook Inc., C.R. BARD, ALN and other companies realize the recovery of filters through an umbrella-shaped structure, but they all share the same problem in their clinical applications: the recovery time window of a present short-term implantable medical instrument, particularly of recoverable vena cava filters, is very short; moreover, as the recoverable vena cava filters are in contact with the inner wall of blood vessels, the recovery time of the filters is short or the filters cannot recovered be successfully due to the embedding of endothelial cells, the migration of smooth muscle and the encapsulation of tissue-like substances, so that the vessel walls may be damaged if the filters are forcibly recovered.
Some researchers tried to prepare a drug coating on the surface of a filter. For example, in Chinese Patent Publication Nos. CN101843531A and CN201870771, a polymer coating is coated on the surface of a filter by antithrombotic and thrombolytic drugs or other drugs, so that the antithrombus and the inhibition to cell embedding are realized by slowly releasing the drugs. Chinese Patent Publication No. CN102330059A employs plasma polymerization to prepare a hydrophobic material (like polyethylene glycol, PEG-L) on the surface of the filter so as to inhibit the embedding of protein and cells. The high-molecular polymer is prepared on a metal substrate in this technical solution, but the polymer coating is likely to crack and fall off during a deployment process of the filter because the metal and polymer have large differences in stiffness, toughness and other physical properties, thereby resulting in insufficient drug administration or new thrombosis sources, and influencing the effectiveness of the filter.
In particular cases, other medical instruments (e.g., intravascular stents) implanted in the human body are also required to be recovered, and the growth of cells on the surfaces of the medical instruments is also required to be inhibited within a certain time. Similar to the vena cava filters, those medical instruments are often fine components made from nickel-titanium alloys, and a coating is required to be manufactured on the fine components. The medical instruments, which are implanted in the human body in an interventional manner, are commonly made from super-elastic nickel-titanium alloys, but the polymer coating is likely to crack and fall off during the deformation and deployment process of the medical instruments, thereby resulting in insufficient drug administration or new thrombosis sources. However, the coating having metallic characteristics may realize better adhesion and ductility on the nickel-titanium alloy surface. Considering that the medical instrument coating in the prior art cannot give consideration to both the better mechanical property and the effective inhibition of cell growth, the present invention employs plasma sputtering deposition to prepare a copper-titanium coating on a surface of a medical instrument. The copper-titanium coating has a good bonding force with a nickel-titanium alloy substrate, a high ductility, the stiffness, toughness and other physical properties, which can meet the mechanical requirements for a large-amplitude deformation of the medical instrument; and the copper-titanium coating continuously releases copper ions in the human body, and thus may effectively inhibit the embedding of cells on the surface of the medical instrument, thereby prolonging the recovery time window of the medical instrument.
At present, the technical problem that a copper-titanium coating capable of releasing copper ions is prepared on the surface of a medical instrument having a fine nickel-titanium alloy component is not well solved. Depositing a coating on a medical instrument having a fine nickel-titanium alloy component by a plasma technology needs to solve the following technical difficulties:
during the preparation process of the coating, plasma is moved to a substrate at a high speed under the action of a sputtering bias voltage, and irons “bombard” the surface of the substrate to generate lots of heat to quickly heat the fine nickel-titanium alloy component, so that the Austenite final temperature Af of the nickel-titanium alloy is increased, but the mechanical properties of the medical instrument are reduced;
during preparing a coating on the surface of the fine nickel-titanium alloy component by a plasma deposition method, as the effective contact area of the plasma with the nickel-titanium alloy surface is small, there is not enough time for ions carrying with energy to quickly spread on the surface, so that a part of ions are “accumulated” or the stress of the coating is concentrated, and the bonding force of the coating thus cannot meet application requirements; and
as the copper-titanium coating releasing copper ions is degradable, the microstructure, bonding force and compactness of the coating directly influence the degradation characteristics of the copper-titanium coating, but the present technological characteristics cannot guarantee the requirements for the ion release rate of the coating; and, as the ratio of two elements in content influences the functionality of the copper-titanium coating, it is required to optimize quality percentages of elements in the coating on the basis of the improvements of deposition methods in the prior art.